sharing: include wwan connection types as broadband

For wwan modems directly attached to the computer.

https://bugzilla.gnome.org/show_bug.cgi?id=732218
sharing: don't shutdown rygel if not autostarted

Rygel is also dbus activated, so we should not call it unless
we know it is running.

https://bugzilla.gnome.org/show_bug.cgi?id=732218